Several recent studies support the premise that genetic differences may predict treatment outcomes. In an early study, an A to G single nucleotide polymorphism (SNP; rs1799971) of the mu opiate receptor gene (OPRM1) predicted 12 week abstinence after treatment of alcohol dependence with naltrexone (Oslin et al 2003). The relationship was such that individuals with at least one copy of the G allele demonstrated lower relapse rates and longer time to return to heavy drinking when treated with naltrexone (Oslin et al 2003). These observations were recently replicated and extended in the multisite COMBINE study, such that individuals with the G allele demonstrated superior outcomes after treatment with naltrexone, in combination with medication management (Anton et al 2008). Laboratory studies have suggested that clinical effects may be related to a greater reduction in the acute rewarding effects of alcohol among individuals with the G allele (Ray & Hutchison 2007) and suggest that the mechanism may be related to a blunting of dopamine release in the VTA (Ramchandani et al 2009). In addition, recent studies with other medications (e.g., topiramate, olanzapine) have found that genetic variables predict treatment outcomes (e.g., Hutchison et al 2006; Hutchison 2008; Seneviratne et al 2009). It is important to note that these gene by treatment interactions are not limited to pharmacological treatments, as recent studies have also suggested that genetic variation may predict responses to psychosocial interventions as well (Feldstein Ewing et al 2009; Hutchison et al 2006).